Sheet material



Patented Mar. 4, 1941 UNITED STATES PATENT OFFICE SHEET MATERIAL No Drawing. Application May 1, 193:, Serial No. 668,808. Renewed January 8, 1946 9 Claims.

This invention relates to sheet material and to a method for preparing the same, and more particularly to the manufacture of thin, transparent, flexible films or sheets for use in the wrapping and packaging of articles of various It has heretofore been suggested that casein might be used in place of gelatine in the preparation of sheet and film material of this character, but to the best of our knowledge no one has heretofore successfully developed a composition and method for the commercial manufacture from casein of thin, clear, transparent sheet or film material having the requisite degree of flexibility and toughness to render the material suitable for wrapping purposes. In the copending application of Edouard M. Kratz and Herman Heckel, Serial No. 630, 406, filed August 25, 1932, however, in addition to describing and claiming a method and apparatus for the manufacture of sheet or film material of this character, there is described but not claimed a composition for use in the preparation of such sheet or film material and a method for preparing such composition.

It is therefore an object of this invention to provide sheet or film material having as its base a protein, which is readily soluble in water or which may be rendered soluble by means of an alkaline or basic reacting substance, the sheet or film material being characterized by its thinness, clear and sparkling transparency, and by its toughness and flexibility, adapting it for use for wrapping purposes.

It is a further important object of this invention to provide a process for preparing such sheet or film material. a

Other and further important objects of this invention will become apparent from the following description and accompanying claims.

The starting material of our invention is a protein, which is readily soluble in water or which may be rendered soluble by means of an alkaline or basic reacting substance. Examples of'suitable proteins of this type are caseins, such as may be derived from milk, soya beans and other sources.

The first step in our process is the purification of the crude casein. Casein is an amphoteric substance having an isoelectric point at a pH value of 4.6. This means that casein forms salts with acids at any pH value numerically lower than 4.6 and also forms salts with bases at any pH value numerically greater than 4.6. According to our invention, the pH value of the casein is adjusted to from 4.6 to 5.0 by adding an acid or a base as required, and is then washed with water in order to remove the resulting inorganic salts and any other readily water soluble impurities. It is not necessary to eliminate the calcium radical entirely if present in combination with casein as calcium caseinate. Thorough washing of the casein is very essential in order to remove all water soluble and crystalline substances, the presence of which in our final sheet material would impart lmdesirable opacity thereto due to surface crystallization.

After the casein has been properly washed with water and its pH adjusted to from 4.6 to 5.0, water is added in the proportion of from 6 to 7 parts of water to one part of casein by weight. The casein is dissolved with a suitable basic substance capable of reacting with the casein to form a water soluble compound. We have found that various caustic alkalies, such as sodium, potassium and lithium hydroxides, ammonium hydroxide and various organic bases, such as alkylamines and hydroxyallwlarnines are suitable for this purpose. As an organic base, we may use an allwlamine, such as the amylamines, ethylene diamine, butylamine, and the like, and a hydroxyalkylamine, such as an ethanolamine, viz. triethanolamine, monoethanolamine, diethanolamine, or a mixture of the mono-, diand tri-ethanolamines, or a polyethanolamine. The poly-ethanolamines are produced by the action of ethylene oxide or triethanolamine. A mixture of one or more of the ethanolamines and an alkali metal hydroxide is likewise satisfactory. A hydroxylamine may also be used.

0f the various basic substances mentioned v above, we prefer to use either caustic potash or triethanolamine, or a mixture of the two. Caustic soda has a tendency to Produce films that become brittle at higher humidities than do films prepared with caustic potash or an ethanolamine. These latter two basic substances produce films that resist the embrittling effect of low humidities. It is probable that triethanolamine has itself a slight plasticizing effect on the film.

The neutralization of the casein mass is carried out bythe addition of the basic substance until the pH value of the solution remains constant at about 6.8, at which point the casein will all be in 5 solution as a' soluble caseinate. The casein may be made to dissolve at pH values below 6.8 but we prefer to adjust the solution to this value because we obtain a better reaction subsequently of the casein solution with formaldehyde when the pH value is at this point. The solution will also be fairly satisfactory if the neutralization is continued to a pH value of from '7 to 7.5, but if this is done with the use of an ethanolamine, the final product will have an unpleasant taste, which is probably due to an excess of the ethanolamine.

of casein, by weight, depending upon the ash content of the casein used. The ash content represents the combined calcium.

While it is very easy to wash out any acidic sub stances which may be combined with the casein, it is much more difficult to wash out the calcium. However, we have found that an ash content of 2 or less gives a satisfactory final product. Since this combined calcium is acting as a base, it combines with a portion of the casein, so that it is not necessary to use as much of the organic base as would otherwise be necessary. As much as 14 parts of triethanolamine may be required to neutralize parts of casein if the casein is substantially free from calcium. Equivalent reacting proportions of the other basic substances may be similarly employed to put the casein into solution and produce the desired pH.

The casein solution, prepared as described above, is next heated to between and F. and agitated preferably for from 4 to 8 hours with a suitable filter aid, such as a diatomaceous earth, kieselguhr, or the like. Thisv period of contact between the casein solution and the filter aid has been found to give the degree of clarity of solution necessary for obtaining a highly transparent film free from specks and blemishes. After the solution has been agitatedwith the filter aid for the required length of time, it is filtered, by any method of filtering which will obtain the proper clarity of solution.

A plasticizer is then added in an amount equal to from 5 to 30%, preferably 20%, of the weight of casein (on a dry basis) used. Any suitable hygroscopic liquid, such as a glycerol, glycerine or a polyglycerol, a water soluble glycol, viz.

ethylene or diethylene glycol, mono-ethyl or butyl ethers of diethylene glycol, or mixtures thereof, or a deliquescent salt, such as potassiumacetate, may be used in place of all or part of the glycerine.

We have found that mixtures of two or more of these plasticizers may advantageously be employed. For instance, a mixture of diethylene glycol and glycerine in the proportions by weight of 1 part of diethylene glycol to 2 to 4 parts of glycerine gives satisfactory results. ing the plasticizer, the viscosity of the solution is adjusted by the addition of water to, an arbitrary value found suitable for forming films or sheet material in accordance with the method described in the application above referred to..

To the clarified and filtered solution, we also may add a number of emulsified substances for imparting certain properties to the finished sheet or film. Various natural or synthetic gums and resins, with or without waxes, mineral oils and the like can be added in the form of emulsions, but we have found that chlorinated diphenyls and gum dammar or mixtures of the chlorinated the trade as Soap H.

- 15% w ght: of ,ithejcasein- (d r have 1a 15 hl ifplasticizing actioriei eir property oflo r' 'e' "t e surface" e'n jion of j After addfactory.

diphenyls with gum dammar, paraflin wax anda refined white mineral oil are particularly satis- Chmrmated enyls and the oxides the-r601 A suitable mixture of sulfonates is known to It comprises certain purified and neutralized hydrocarbon sulfonic acids obtained as a by-product in the manufacture of the so called white" oils. In such manufacture, a lubricant fraction of the oil is treated with fuming sulfuric acid. Some of the resulting sulfonic acids are soluble in the oil and others separate as a black sludge with the excess acid. The oil portion is neutralized with caustic soda and extracted with 50% alcohol.v The ex- I tracted material, consisting mostly of the sodium sulfonates of the hydrocarbons, after further alcoholic I purification to eliminate,the oil and sodium sulfate, is known as Soap Hand is both oil and water soluble. and mixes well with the" gums and resins used. Its function in our-composition is to act as an emulsifying agent'a'nd it may be replaced by other suitable emulsifying agents, if desired, such as the triethanolamine meant, that after the solution is' applied to such I surface, it has no tendency to coalesce or oil spot. Soap H and sulfonated castor mama-y be,

added either singlyor together in amounts the solution. V v

Before adding these resinous substances to-the vcasein solution, they are preferablyameltedato- V The followingillustrates our preferred proportions, but, ouriinvention is not I to be construed as'lir'nitedjto the exact propor gether with heat.

tions shown, since obviously they maybe-varied.

somewhat:

Gum dammar parts by weight' 2 Chlorinated diphenyl parts 29/: Soap H do 5 Cyclohexan'ol do 1 From 5 to 50%, but preferably about '11% of this melted mixture, based upon the dry weight of the casein used, is added to the casein solution. The function of, Soap-H in the above formula is that of an emulsifying agent. It may be replaced by other suitable emulsifying agents, such as triethanolamine oleate. a

The above resinous mixture is melted and poured into a-small quantity of casein solution kept at approximately to F., with constant agitation, and the resulting emulsion is then transferred to the main portion of the casein solution.

Toobtainaclearfilm,itisnecessarythatthe gumsandresinsbehighlydispersedandinorder to accomplish this, a very large proportion of the emulsifying agent is n. We prefer to use about one part of the emulsifying agent toonepartofthemixtureofresinsorgumsto be emulsified. Cyclohexanol is added to the mixture when Soap H" is used because cyclohexanol has the property of assisting dispersions made with Soap H. ,Cyclohexanol may be omitted when other emulsifying agents are used. In place of cyclohexanol, other dispersing assistants, such as methyl alcohol, may be used.

The following example is given as an illustration of suitable proportions, but our invention should not be construed as limited to these proportions and specific ingredients, since other substances may be submtuted as explained above, and the proportions may be varied within considerable limits:

Preferred Broader range Parts by Paris by Protein. Casein (purified) ica 600 Tm "JII so 45 to as Plasticizu: Glyccrine 12c 30 to 180 is o m 150 15 0 to 150 Soap 11 so 0 to 300 Berlin (cyclobenuol) 6 0 to 60 The combined eifect of the gums, resins, and

emulsifying agent is to give the film more body, greater brilliance, or sheen, greater strength and better resistance to low humidlties. For exame, if the washed casein be dissolved with sodium hydroxide, a fihn is obtained which becomes brittle at approximately 35% relative humidity. The combined effect of the resins and emulsifying agents will lower the brittle point to about 30% relative humidity, and when our preferred .basic substances, potassium hydroxide or triethanolamine, are used as the dissolving agent for the casein, the resulting film will withstand relative humidities as low as 17 to 20% without becoming brittle.

In casting a composition such as described into sheets or films, a suitable insolubilizing agent, such as an aldehyde, or the like, is added. The effect of such an agent is to render the caseinate insoluble in water and to strengthen the film greatly. For this purpose, we prefer to use a 6% solution of formaldehyde in water. A stronger solution will tend to cause precipitation of the casein at the time the solutions are mixed. v Our preferred proportion for these solutions is about 1 part -of the 6% formaldehyde solution to parts by volume of the casein solution. Since this is more than sufllcient formaldehyde to give the maximum insolubilizing action, lesser quantitles of formaldehyde may therefore be used. The two solutions should be thoroughly mixed just before use and then promptly cast in continuous films or formed into sheets, since the mixture sets in a few minutes.

It is preferable to mix the solutions continuously in small quantities and immediately and continuously flow the mixtures onto a suitable forming belt, A belt having a coating of cellulose nitrate will be satisfactory for this purpose. A suitable machine for use in forming this composition into sheets is described in the copending application of Edouard M. Kratz and Herman Heckel, Serial No. 630,406, filed August 26, 1932.

After being cast onto the forming or carrier belt, the film on the belt is subjected to a drying operation by passing the belt through heated drier chambers, under controlled temperature and humidity conditions. The film is thereby dried and is then stripped from the carrier belt and wound into a roll in a continuous operation.

The reaction between the casein and organic amine is similar to that between casein and an alkali metal hydroxide and results in the formation of a caseinate of the particular organic amine used. This reaction product is soluble in water. The resinous substances added, however, such as a chlorinated diphenyl, dammar gum, or the like, are not water soluble but may be highly dispersed in the solution of the caseinate by means of suitable dispersing and emulsifying agents,

" oils, such as linseed or tung oil, may also be incorporated into the composition.

Any suitable dye may be used if a colored sheet or film material is desired. For instance, Metanil Yellow will give a satisfactory yellow or gold colored sheet.

The final film or sheet material is characterized by its clear transparency, its homogeneity and its freedom from specks, opaque particles or other blemishes. For most purposes the sheet or film material is cast as a very thin pellicle of the same relative thinness as cellulose acetate and cellulose xanthate, or regenerated cellulose, sheet material. Our product is flexible and tough and possesses a relatively good tensile strength. When made from our preferred composition, our sheet or film material is satisfactorily resistant to ordinary climatic changes in temperature and relative humidity and therefore well suited for wrapping and display purposes.

We are aware that numerous details of the process may be varied through a wide range without departing from the principles of this invention, and we, therefore, do not purpose limiting the patent granted hereon otherwise than necessitated by the prior art.

We claim as our invention:

1. A thin, clear, transparent, brilliant sheet or film having sufllcient flexibility and toughness to adapt it for wrapping purposes, comprising a reaction product of a caselnate and formaldehyde, a chlorinated diphenyl, an emulsifying agent and a plasticizer.

2. A thin, clear, transparent, brilliant sheet or fllm having suflicient flexibility and toughness to adapt it for wrapping purposes, comprising a reaction product of triethanolamine caseinate and formaldehyde, a chlorinated diphenyl, an alkali metal sulfonate of a hydrocarbon oil, and a water soluble mixture of a glycol and 9, glycerol.

3. A thin, clear, transparent, brilliant sheet or film having a high degree of flexibility and toughness, comprising a homogeneous mixture of an insolubilized caseinate, a chlorinated diphenyl, dammar gum, a hydrocarbon sulfonate, and glycerine.

4. A thin, clear, transparent, brilliant sheet or film having a high degree of flexibility and toughness, comprising a homogeneous mxture of an insolubilized triethanolamine caseinate, a chlorinated diphenyl, dammar gum, a hydrocarbon sulfonate, and glycerine,

. 5. A thin, clear, transparent, brilliant sheet or film having a high degree of flexibility and toughness, comprising a homogeneous mixture of an insolubilized caseinate, a chlorinated .diphenyl,

dammar'gum, an emulsifying agent and a plasticizer. p v p 1- 6. A thin clear transp arent brilliant sheet or film suitable for wrapping purposes comprising anv hydroxyalkylamine caseinate" 'insolubilized' by I formaldehyde and a chlorinated diphenylp 1 7. A thin clear, transparent sheetor film suit- I able for wrapping purposes comprising a reaction product of triethanolamine caseinate and formal- -dehyde and a chlorinated diphenyl.

'8. As a new composition of matter, asuspensoid comprising water, a water-soluble caseinate, a water insoluble resinous substance, and an emulsi a fying agent, the continuous phase of the susp'ens oid comprising water and the discontinuous .phase J consisting essentially of particles of solids comprisingparticles of caseinate and particles of resinous substance of'such size that they do not settle. i

substance as an" ingredient,in the'discontinuo'us phasein minor amount, theparticles of caseinate and resinous substances being ,of such size that theyfdo not settle; k l p 1 EDOUARD KRATZ..

EUGENE BROWNING. I ERICHI'GEBAUER-FUELNEGG. 

